Acold and dry biome characterized by moses, grasses and small shrubs

littering streams           is the answer

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

there really is life in the deepest part

c. heat from the poles back down towards the equator.